1. Field of the Invention
The present invention relates to laminated substrates which are used for various kinds of electronic products, wherein each electrode of one substrate is brought into conduction to the wiring pattern of the other substrate via a through hole formed in the substrates, and further relates to a pad-type data input unit which uses the laminated substrates and is used for a computer or the like.
2. Description of the Related Art
In recent years, many computers called a note-type computer have been used in an office or in a home for the purpose of saving a space and many pad-type data input units operated by lightly tracing with a finger have been adopted and put into commercially practical use as an input unit when a cursor or the like displayed on the screen of the computer is moved.
FIG. 5 shows a cross sectional view of a structure of a conventional pad-type data input unit 40.
The above-mentioned type data input unit 40 is constituted by a sensor sheet 10 for detecting coordinates, a printed circuit board (PCB) 21 on which a wiring pattern is printed, and a face sheet 30 to which a finger or the like is directly touched.
The above-mentioned sensor sheet 10 has a sensor substrate 2 for detecting the coordinates to which the finger is touched and the above-mentioned sensor substrate 2 is formed of material such as polyethylene telephthalate (PET) or the like and has X electrodes 12 and Y electrodes 13 formed on both surfaces thereof. Further, resist films 6 and 7 are formed on both surfaces of the above-mentioned sensor substrate 2, respectively, and the underside resist film 7 is bonded and fixed to the above-mentioned PCB 21 by a bonding layer 8.
A plurality of through holes 23 are formed along the periphery of the PCB 21, and a land 29 for bonding the X electrode 12 formed on the above-mentioned sensor substrate 12 to the wiring pattern of the PCB 21 via the above-mentioned through hole 23 is formed.
Further, through holes 35 are formed also in the sensor sheet 10 such that each of them communicates with each through hole 23 of the above-mentioned PCB 21 and the X electrode of the above-mentioned sensor substrate 2 side is brought into conduction to the land 29 of the above-mentioned PCB 21 side by filling a conductive material 11 such as conductive resin or the like in the through holes 35 and 23 from the sensor substrate 2 side.
Furthermore, the above-mentioned face sheet 30 is fixedly bonded to the obverse surface of the above-mentioned sensor sheet 10 side by an adhesive or the like and parts such as an IC or the like necessary for performing data input processing are mounted on the surface (underside surface in the drawing) on which the wiring pattern of the above-mentioned PCB 21 is formed.
In the data input unit 40 constituted as described above, when an operator lightly slides a finger on the face sheet 30, part of a line of electric force heading for the Y electrode 13 from the X electrode 12 in the X electrode 12 and the Y electrode 13 formed on the above-mentioned sensor substrate 2 is absorbed by the finger of the operator to produce a phenomenon that the line of electric force absorbed by the Y electrode 13 is reduced to change electrostatic capacity, whereby a coordinate position touched by the finger can be detected based on the current output value of the sensor substrate 2 which is changed according to a change in the electrostatic capacity.
In the conventional data input unit 40 shown in FIG. 5, the above-mentioned PCB 21 is a double-sided substrate having the wiring patterns on both surfaces thereof and the lands 28 formed on both surfaces of the substrate are connected and brought into conduction through the through hole 23 and the lands 29 formed on both surfaces of the substrate are also connected and brought into conduction through the through hole 23. Therefore, when the X electrode 12 of the above-mentioned substrate 2 is bonded to the land 28 of the above-mentioned PCB 21, the above-mentioned conductive material 11 is not required to be extended to the land 28 of the underside surface, and the PCB 21 and the sensor substrate 21 can be brought into conduction by joining the conductive material 11 to the land 29 of the obverse surface of the PCB 21.
However, the above-mentioned conventional data input unit 40 has the following problems.
1) The PCB 21 has wiring patterns printed on both surfaces thereof and hence is required to form a conductive material made of metal or the like on the inner wall surface of the through hole 23 so as to join the wiring patterns printed on both surfaces of the substrate, which increases costs for manufacturing the PCB 21.
Therefore, if a PCB having a wiring pattern formed only on one side of the substrate is used, the above-mentioned problem can be solved.
2) However, if a PCB having a wiring pattern formed only on one side of the substrate, that is, on the side on which parts are mounted (underside surface side in the drawing), is used instead of the above-mentioned double-sided PCB 21, it is necessary to extend the conductive material 11 supplied from the sensor substrate 2 side to the land 28 of the surface on which the parts of the PCB 21 are mounted.
However, if the conductive material 11 is filled in the through hole 35 from the sensor substrate 2 side, the air in the through hole 35 can not be released outside but remains inside and forms a space as shown by a numeral 31 in FIG. 5 and hence the air and the solvent gas contained in the conductive material 11 build up the resistance to produce the following problems: that is, the conductive material 11 is not extended to the land of the underside surface shown in the drawing of the PCB 21, or, after the conductive material 11 is dried and cured, the above-mentioned space 31 is thermally expanded to bulge and break the conductive material 11 in the through hole, and further, it is impossible to visually check the conductive material 11 from the outside to see that the conductive material 11 completely continues in the through hole.
Further, in order to completely pass the conductive material 11 supplied to the through hole 35 from the sensor substrate 2 side into the through hole 23, there is an other method by which the conductive material 11 is supplied to the through hole 35 from the sensor substrate 2 side and is sucked from the underside surface side of the PCB 21. However, this method needs a sucking unit and increases the cost of the unit.
3) In this kind of data input unit, a face ground for releasing static electricity generated when a face sheet 30 is touched by a finger is required. As shown in FIG. 5, when the PCB 21 having wiring patterns on both surfaces thereof is used, the face ground 32 exposed at the edge part of the substrate can be formed by using the wiring pattern on the surface of the PCB 21. However, when the PCB 21 having a wiring pattern only on the underside surface is used, the face ground can not be formed on the surface of the PCB 21. The face ground formed on the reverse surface of the PCB can not sufficiently release static electricity charged on the face sheet 30.